The present invention relates to catheters for insertion into a body lumen. More particularly, the present invention relates to "focal" balloon dilatation catheters for use in the vascular system. As used herein, "focal" balloons are balloons which focus or concentrate expansive energy at one or more predetermined regions along the surface of the balloon.
Prior art vascular dilatation balloons on typical dilatation catheters tend to fall into one of two broad classes. Most are considered noncompliant balloons, formed from a generally nondistensible material such as polyethylene. The perceived advantage of the noncompliant balloons is that they exhibit a substantially uniform exterior inflated profile which remains substantially unchanged upon incremental increases in inflation pressure. In theory, noncompliant balloons are advantageous because they allow the introduction of increased inflation pressure to break particularly calcified lesions, yet retain a predictable inflated profile so that damage to the surrounding native lumen is minimized.
Certain compliant balloons are also known in the art. A compliant balloon is one which is able to grow in diameter in response to increased inflation pressure. One difficulty with compliant balloons, however, is that inflation within a difficult lesion can cause the balloon to inflate around the plaque to produce a generally hourglass-shaped inflated profile. This can result in damage to the native vessel adjacent the obstruction, while at the same time failing to sufficiently alleviate the stenosis.
In use, both the compliant and noncompliant balloons are generally inflated within a vascular stenosis to a rated inflation pressure. At that pressure, the configuration of most balloons in an unrestricted expansion is cylindrical. The balloon may be subsequently inflated to a higher inflation pressure if that is desirable in the clinician's judgment. However, the clinician has no effective way to assess the actual inflated diameter of the balloon in vivo based upon the unconstrained in vitro balloon specifications. The in vivo expansion characteristics of the balloon may track or deviate from the in vitro specifications depending upon the morphology of the lesion and the appropriateness of the selected balloon size. The clinician may know only generally or not at all the degree of calcification of the lesion, the symmetry or asymmetry, whether the lesion is soft or resilient, or other variations which affect inflation. In applications where a relatively accurate inflated diameter is desired, such as in certain dilatations or in the implantation of tubular stents, the clinician using prior dilatation balloons thus may not have enough information about the dilatation characteristics of a particular lesion to optimize the dilatation or stent implantation procedure.
Therefore, there exists a need in the art for a vascular dilatation catheter with a balloon which is able to grow predictably in response to increased inflation pressure, and the expansion of which the clinician can observe in real time in comparison to a known diameter reference.